Luminescent solar concentrators are known in the art and act to trap and collect light from luminescent centers dispersed in a planar sheet. Luminescent concentrators utilize the total internal reflection in the wave-guide to trap a portion of the light emitted from the luminescent centers. The luminescent centers reradiate longer wavelength light in a 360 degree solid angle and so are inefficient in directing light to one edge of the plate or to a small region of the edge.
One example of a solar concentrator known in the art utilizes a hologram and a prism or plate; see, e.g., U.S. Pat. No. 4,863,224, issued to Afian et al. However, this solar concentrator needs to be aligned to the sun and does not provide for any passive solar tracking ability.
Also known in the art is a light gathering device comprising a hologram and a total reflection surface for a collecting monochromatic light at a single angle of incidence; see, e.g., U.S. Pat. No. 5,268,985, issued to Ando et al. However, Ando et al employ a single angle of incidence and a single wavelength, and thus require a tracking mechanism and cannot utilized the entire solar spectrum.
Yet another concentrator known in the prior art is an electromagnetic wave concentrator; see, e.g., U.S. Pat. No. 4,505,264, issued to Tremblay. The electromagnetic wave concentrator utilizes a multidielectric guiding plate to concentrate electromagnetic energy. This invention has the disadvantage of multiple reflection losses in the guiding plate and high absorption losses in some of the more cost effective embodiments. Also this invention posses difficult optical fabrication problems and hence is more expensive to fabricate.
U.S. Pat. No. 5,877,874, issued Mar. 2, 1999, to the present inventor, discloses a device for concentrating solar radiation, which employs a hole graphic planar concentrator (HPC) for collecting and concentrating optical radiation. The HPC comprises a planar, highly transparent plate and at least one multiplexed holographic optical film mounted on a surface thereof. The multiplexed holographic optical film has recorded therein a plurality of diffractive structures having one or more regions which are angularly and spectrally multiplexed. Two or more of the regions may be configured to provide spatial multiplexing, While the teachings of that patent are certainly useful for its intended purpose, improvements thereover are sought; the present invention represents such an improvement.
There remains a need for a solar concentrator that decreases energy losses in the concentration of solar radiation and that utilizes a substantial portion of the solar spectrum while reducing or eliminating tracking requirements.